As computer technology has advanced and the use of the Internet has spread, it has become possible to present clear, detailed map images on display screens of computers. In computers, images are usually displayed on computer screens, by implementing various types of image display software (viewer). Map images can be displayed not only on the computer screens, but also on the screens of portable terminals, such as car navigation systems and mobile phones. Further, in CAD systems, images for presenting design information (arrangements and connections) for semiconductor circuits and machines are conventionally displayed on display screens. Furthermore, in optical or electronic microscopes, images of the surface states of micro substances are reproduced on display screens.
These images are displayed while being enlarged or reduced by the operations of operators of respective apparatuses, under the implementation of image display software (viewer) . In other words, the displaying range of the image on the display screen can be arbitrarily altered. Now, assume that a map image is displayed on a display screen. Assume that at first the displayed map image is greatly magnified. That is, the map image is enlarged at a certain magnification. In other words, it means that the range (area) of the map displayed on the display screen is narrow. Next, suppose a case wherein the map image is moved from a current position (starting position) on the screen, searching for another targeted position that is currently not visible on the screen.
In this case, conventionally, the following two methods can be employed. According to the first method, the map image displayed on the display screen is sequentially moved, without changing the current magnification, until the targeted position is reached. According to the second method, the image is first displayed at a smaller magnification until the targeted position is displayed on the display screen, and after the targeted position is placed to the center of the map image, the image is enlarged to a certain magnification.
In the case of the first method, the moving of the image must be repeated many times until the targeted position is found. Further, since the targeted position is not always present at a position along the image moving direction, it is necessary to repeat the moving of the image several times, changing the moving direction during the process. Particularly in a case wherein an area for a search (targeted position) is unfamiliar, the repetition tends to be increased.
In the case of the second method, since the magnification is first reduced, the targeted position is easily found on the image after it is reduced. However, when the magnification of the image is reduced (or enlarged), the viewer usually reduces (or enlarges) the image, employing the center of the displayed image as a reference (a virtual center). Therefore, in the case wherein the current position before the image reduction is located in the center of the displayed image, and after the image is reduced, the display area on the side opposite to the direction in which the image map is moved to the targeted position becomes an area that is not actually required to view and is unnecessary. That is, it is not possible to display the image, after the magnification is reduced, of only the area between the current position and the targeted position or a region including that area as a greater part. This applies to a case wherein the magnification of the image including the targeted position is increased. That is, in the case wherein the targeted position is placed at the center of the displayed image, the display area in the enlarged image on the side opposite to the direction in which the map image is moved to the initial current position (starting point) becomes an area that is not actually required to view and is unnecessary. In order to reduce the size of such an unnecessary area, the setup of the center (virtual center) of the magnification change, and the magnification change must be alternately repeated a number of times. This problem arises not only for a map image, but also for a CAD image, a microscope image or the like.